Intercalation agent free compositions useful to make nanocomposite polymers

ABSTRACT

A method for preparing a filler composition useful for preparing a nanocomposite polymer is provided. The method includes a first step of dispersing a water dispersible filler material in a liquid comprising water to form a dispersion and a second step of replacing at least a portion of the water of the liquid with an organic solvent. The resulting filler composition features a water concentration of the liquid of less than six percent by weight, and the average size of at least one dimension of the filler material is less than two hundred nanometers upon examination by transmission electron microscopy of a representative freeze dried sample of the dispersion of the first step. A nanocomposite polymer, particularly and epoxy resin composition, can be prepared by mixing the above-made filler composition with one or more polymer, polymer component, monomer or prepolymer.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a §371 application of PCT International Patent ApplicationNumber PCT/US2007/024030 filed Nov. 16, 2007, and claims priority fromprovisional application Ser. No. 60/861,872 filed Nov. 30, 2006, each ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The instant invention is in the field of nanocomposite polymers. Morespecifically, the instant invention is in the field of compositionsuseful to make nanocomposite polymers and methods of preparing suchcompositions.

Delaminated or exfoliated cation exchanging layered materials (such asdelaminated 2:1 layered silicate clays) can be used as reinforcingfiller in a polymer system. Such polymer systems are known as“nanocomposites” when at least one dimension of the filler is less thantwo hundred nanometers. Nanocomposite polymers generally have enhancedmechanical property characteristics vs. conventionally filled polymers.For example, nanocomposite polymers can provide both increased modulus,lower density, improved clarity, lower coefficient of thermal expansionand in some instances increased impact toughness, a combination ofmechanical properties that is not usually obtained using conventionalfillers such as talc.

Transmission electron photomicrographs of nanocomposite polymers havinga cation exchanging layered material filler typically show a dispersionof multiple layer units (e.g., from one to five layers per unit) of thecation-exchanging layered material in the polymer matrix. However, it isgenerally desired to achieve a high degree of delamination of thecation-exchanging layered material. Ideally the degree of suchdelamination is so extensive that only single layer units of thecation-exchanging layered material are present. If the cation-exchanginglayered material is not sufficiently delaminated, then the mechanicalproperty improvement of the polymer composite will usually be no betterthan if conventional micron sized filler is dispersed in the polymer.

Cation exchanging layered materials are often treated with an organiccation (usually an “onium”) as an “intercalation agent” to facilitatedelamination of the cation exchanging layered material before the cationexchanging layered material is blended with a polymer (see, for exampleU.S. Pat. No. 5,973,053). However, the use of such intercalation agentsincreases the cost of the nanocomposite polymer and can act as aplasticizer for the polymer and thereby limit the strength, thermalresistance and stability of the nanocomposite polymer. It would be anadvance in the nanocomposite polymer art if the use of suchintercalation agents could be eliminated while never-the-lessmaintaining a sufficient degree of delamination of a cation exchanginglayered material to produce a lower cost nanocomposite polymer having abetter balance of physical property improvements.

SUMMARY OF THE INVENTION

The instant invention provides a solution to the above stated problem.The instant invention provides an intercalation agent free fillercomposition useful to make a nanocomposite polymer having increasedflexural modulus with no reduction in toughness or glass transitiontemperature. In one embodiment, the instant invention is a method forpreparing a filler composition useful to prepare a nanocompositepolymer, comprising the steps of: (a) dispersing a water dispersiblefiller material in a liquid comprising water to form a dispersion; (b)replacing at least a portion of the water of the liquid with an organicsolvent so that the water concentration of the liquid is less than sixpercent by weight to form the filler composition, the average size of atleast one dimension of the filler being less than two hundred nanometersupon examination by transmission electron microscopy of a representativefreeze dried sample of the dispersion of step (a).

In another embodiment, the instant invention is a method for preparing ananocomposite polymer by the step of: mixing the filler composition ofthe instant invention with one or more polymer, polymer component,monomer or prepolymer to produce a polymer containing a filler having anaverage size of at least one dimension of the filler of less than twohundred nanometers upon examination by transmission electron microscopyof a representative sample of the polymer.

In another embodiment, the instant invention is an epoxy resincomposition useful for making an epoxy nanocomposite polymer, the epoxyresin composition made by the steps of: (a) mixing an epoxy resin withthe filler composition of the instant invention to form an epoxy resinmixture; and (b) removing most of the organic solvent from the epoxyresin mixture to form the epoxy resin composition.

In yet another embodiment, the instant invention is an epoxynanocomposite polymer made by the steps of: (a) mixing an epoxy resincuring agent with the epoxy resin composition to form an uncured epoxynanocomposite polymer; and (b) curing the uncured epoxy nanocompositepolymer to form the epoxy nanocomposite polymer containing filler havingan average size of at least one dimension of the filler of less than twohundred nanometers upon examination by transmission electron microscopyof a representative sample of the epoxy nanocomposite polymer.

In still another embodiment, the instant invention is a nanocompositepolymer, made by the steps of: mixing the filler composition of theinstant invention with one or more polymer, polymer component, monomeror prepolymer to produce a polymer containing a filler having an averagesize of at least one dimension of the filler of less than two hundrednanometers upon examination by transmission electron microscopy of arepresentative sample of the polymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a transmission electron micrograph of an epoxy nanocompositemade using a composition of the-instant invention;

FIG. 1B is a transmission electron micrograph of the epoxy nanocompositeof FIG. 1A at higher magnification.

FIG. 2 is a transmission electron micrograph of a prior art epoxynanocomposite;

FIG. 3 shows the X-ray diffraction patterns of n-MMT dried at 110° C.,for n-MMT, for g-MMT dried at 110° C., for g-MMT and for Pristine MMT;

FIG. 4 shows the X-ray diffraction patterns of Epoxy/n-MMT, forEpoxy/d-MMT, for MMT mixed with epoxy curing agent DDS and for PristineMMT; and

FIG. 5 shows the dynamic-mechanical analysis scans for Neat epoxy, forEpoxy/d-MMT and for Epoxy/n-MMT.

DETAILED DESCRIPTION

In one embodiment, the instant invention is a method for preparing afiller composition, the filler composition useful to prepare ananocomposite polymer, comprising the steps of: (a) dispersing a waterdispersible filler material in a liquid comprising water to form adispersion; (b) replacing at least a portion of the water of the liquidwith an organic solvent so that the water concentration of the liquid isless than six percent by weight to form the filler composition, theaverage size of at least one dimension of the filler material being lessthan two hundred nanometers upon examination by transmission electronmicroscopy of a representative freeze dried sample of the dispersion ofstep (a). The water dispersible filler material can include high aspectratio particles (plates, sheets, fibers, and ribbons), medium aspectratio particles and low aspect ratio particles (sand like or spheroidalin shape) of various compositions and morphologies. The gist of theinstant invention is the conversion of a preferably hydrophilicinorganic colloid into a composition that can be used to prepare ananocomposite polymer, by dispersing the water dispersible fillermaterial in a liquid comprising water (and often just water) to form adispersion, then replacing most of the water with an organic solvent.For example and without limitation thereto, the concentration of waterdispersible filler material of a water dispersion of the waterdispersible filler material can be increased by centrifugation and thena water miscible organic solvent can be added to the concentrated waterdispersible filler material to form the filler composition of theinstant invention. Preferably, the water concentration of the fillercomposition thus formed is further reduced by adding more organicsolvent (which may or may not be as water miscible as the initial addedorganic solvent) followed by concentration of the filler material by,for example and without limitation thereto, centrifugation, to produce afiller composition having a water concentration reduced thereby. Afiller composition having an even lower water concentration can beprepared by repeating the operation of the preceding sentence one ormore times. A highly preferred filler material is a cation exchanginglayered material wherein the cation exchanging capacity of the cationexchanging layered material is less than twenty percent exchanged withan organic cation (more preferably the cation exchanging capacity of thecation exchanging layered material is essentially free of organiccation).

The water dispersible filler material can, without limitation thereto,be selected from the group consisting of natural or synthetic bentonite,montmorillonite, hectorite, fluorohectorite, saponite, stevensite,nontronite, sauconite, glauconite, vermiculite, chlorite, mica,hydromica, muscovite, biotite, phlogopite, illite, talc, pyrophillite,sepiolite, attapulgite, palygorskite, berthierine, serpentine,kaolinite, dickite, nacrite, halloysite, allophane, hydrotalcite,pyroaurite, calcite, wollastonite, various colloidal borates, silicates,aluminates, phosphates, sulfates, sulfides and halides, as well asvarious synthetic sols, colloids, gels and fumes made, for example andwithout limitation thereto, adding acid to a sodium silicate or sodiumaluminate solution (and mixtures), or adding base to metal saltsolutions, or by hydrolyzing metal alkoxides.

The organic solvent initially added to the dispersion of the waterdispersible filler material in water is preferably miscible with waterin all proportions. Examples of suitable organic solvents include,without limitation thereto, alcohols, ketones, glycols, ethers, glycolethers, glymes (glycol dimethyl ethers), butanediol, hexanediol, amines,polyether polyamines, N-methylformamide, N-methylpyrrolidone,dimethylformamide, diethanolamine, triethanolamine, polyglycols andmixtures thereof. Water can be removed from the mixture of the organicsolvent and the dispersion of the water dispersible filler material inwater by any suitable method such as, without limitation thereto,distillation, centrifugation, filtration, dialysis and evaporation.

As discussed above, it is known that delaminated or exfoliated cationexchanging layered materials (such as delaminated 2:1 layered silicateclays) can be used as reinforcing filler in a polymer system. Suchpolymer systems are known as “nanocomposites” when at least onedimension of the delaminated cation exchanging layered material is lessthan two hundred nanometers. Typically, transmission electron microscopyof a nanocomposite polymer shows a few or no single layers ofdelaminated cation exchanging layered material but rather mostlymultiple layer stacks of cation exchanging layered material.Never-the-less, such nanocomposite polymers generally have enhancedmechanical property characteristics versus conventionally filledpolymers. For example, such nanocomposite polymers can provide bothincreased modulus and increased impact toughness, a combination ofmechanical properties that is not usually obtained using conventionallysized fillers. Although the filler of a nanocomposite polymer is usuallya cation exchanging layered material it should be understood that, asdiscussed above, any filler can be used in the instant invention as longas the filler is water dispersible and wherein at least one dimension ofthe filler averages less than two hundred nanometers.

The term “cation exchanging layered material” means layered oxides,sulfides and oxyhalides, layered silicates (such as Magadiite andkenyaite) layered 2:1 silicates (such as natural and syntheticsmectites, hormites, vermiculites, illites, micas, and chlorites).Cation exchanging layered materials are often treated with an organiccation (usually an “onium”) to facilitate delamination of the cationexchanging layered material when it is blended with a polymer (see, forexample U.S. Pat. No. 5,973,053). Conventionally, the layered materialis “fully exchanged” or “overexchanged”, i.e., the exchangeable cationsof the layered material are essentially fully replaced by onium ions orthe exchangeable cations of the layered material are essentially fullyreplaced by onium ions and the material contains additional onium ions.The use of such onium ions as intercalation agents increases the cost ofthe nanocomposite polymer and these agents can act as a plasticizer forthe polymer and thereby limit the strength and thermal resistancestability of the nanocomposite polymer. Thus, it would be an advance inthe nanocomposite polymer art if the use of such intercalation agentscould be eliminated.

The cation exchange capacity of a cation exchanging layered materialdescribes the ability to replace one set of cations (typically inorganicions such as sodium, calcium or hydrogen) with another set of cations(either inorganic or organic). The cation exchange capacity can bemeasured by several known methods, most of which perform an actualexchange reaction and analyzing the product for the presence of each ofthe exchanging ions. Thus, the stoichiometry of exchange can bedetermined on a mole percent basis. It is observed that the variouscation exchanging layered materials have different cation exchangecapacities which are attributed to their individual structures and unitcell compositions.

The term “organic cation” means a cation that contains at least onehydrocarbon radical. Examples of organic cations include, withoutlimitation thereto, phosphonium, arsonium, sulfonium, oxonium,imidazolium, benzimidazolium, imidazolinium, protonated amines,protonated amine oxides, protonated betaines, ammoniums, pyridiniums,aniliniums, pyrroliums, piperidiniums, pyrazoliums, quinoliniums,isoqunoliniums, indoliums, oxazoliums, benzoxazoliums, andquinuclidiniums. A typical example of an organic cation is a quaternaryammonium compound of formula R₁R₂R₃R₄N⁺, wherein at least one of R₁, R₂,R₃ or R₄ contains ten or more carbon atoms. The term “organic cation”also includes a protonated amine which can be prepared, for example andwithout limitation thereto, by the contact of the cation exchanginglayered material with an acid followed by contact of the cationexchanging layered material with an organic amine to protonate theamine.

In another embodiment, the instant invention is a method for preparing ananocomposite polymer by the steps of: mixing the filler composition ofthe instant invention with one or more polymer, polymer component,monomer or prepolymer to produce a polymer containing a filler having anaverage size of at least one dimension of the filler of less than twohundred nanometers upon examination by transmission electron microscopyof a representative sample of the polymer. For example and withoutlimitation thereto, when the monomer comprises an epoxy resin, then thefiller composition can be mixed with the epoxy resin to form a mixturewith the filler composition which mixture can then be devolatilized toremove organic solvent and then cured to produce an epoxy nanocompositepolymer (the term “devolatilized” includes evaporation of the organicsolvent). As an additional example and without limitation thereto, thefiller composition can be blended with a molten thermoplastic polymer inan extruder having a subsequent section for removing most of the organicsolvent of the filler composition.

In a related embodiment, the instant invention is an epoxy resincomposition useful for making a cured epoxy nanocomposite polymer, theepoxy resin composition made by the steps of: (a) mixing an epoxy resinwith the filler composition of the instant invention to form an epoxyresin mixture; and (b) removing organic solvent from the epoxy resinmixture to form the epoxy resin composition. A cured epoxy nanocompositepolymer according to the instant invention can be made by mixing anepoxy resin curing agent with the above described epoxy resincomposition to form an uncured epoxy nanocomposite polymer followed bycuring the uncured epoxy nanocomposite polymer to form an epoxynanocomposite polymer containing filler having an average size of atleast one dimension of the filler of less than two hundred nanometersupon examination by transmission electron microscopy of a representativesample of the epoxy nanocomposite polymer.

The epoxy resin component used to prepare the epoxy resin composition ofthe instant invention is a polyepoxide. The polyepoxide compound usefulin the practice of the present invention is suitably a compound whichpossesses one or more vicinal epoxy group per molecule, i.e. at leastone 1,2-epoxy group per molecule.

In general, the polyepoxide compound is a saturated or unsaturatedaliphatic, cycloaliphatic, aromatic or heterocyclic compound whichpossesses at least one 1,2-epoxy group. The polyepoxide compound can besubstituted, if desired, with one or more non-interfering substituents,such as halogen atoms, hydroxy groups, ether radicals, lower alkyls andthe like.

The polyepoxide compounds useful in the present invention are well knownin the art. Illustrative polyepoxide compounds useful in the practice ofthe present invention are described in the Handbook of Epoxy Resins byH. E. Lee and K. Neville published in 1967 by McGraw-Hill, New York andU.S. Pat. No. 4,066,628, incorporated herein by reference.

Particularly useful polyepoxide compounds which can be used in thepractice of the present invention are polyepoxides having the followinggeneral formula:

wherein R is substituted or unsubstituted aromatic, alphatic,cycloaliphatic or heterocyclic polyvalent group and n has an averagevalue of from 1 to less than about 8.

The epoxy resins useful in the present invention may include, forexample, the glycidyl polyethers of polyhydric phenols and polyhydricalcohols. As an illustration of the present invention, examples of knownepoxy resins that may be used in the present invention, include forexample, the diglycidyl ethers of resorcinol, catechol, hydroquinone,bisphenol, bisphenol A, bisphenol AP (1,1-bis(4-hydroxylphenyl)-1-phenylethane), bisphenol F, bisphenol K, tetrabromobisphenol A,phenol-formaldehyde novolac resins, alkyl substitutedphenol-formaldehyde resins, phenol-hydroxybenzaldehyde resins,cresol-hydroxybenzaldehyde resins, dicyclopentadiene-phenol resins,dicyclopentadiene-substituted phenol resins tetramethylbiphenol,tetramethyl-tetrabromobiphenol, tetramethyltribromobiphenol,tetrachlorobisphenol A and any combination thereof.

Examples of diepoxides particularly useful in the present inventioninclude diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane (generallyreferred to as bisphenol A) and diglycidyl ether of2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane (generally referred to astetrabromobisphenol A). Mixtures of any two or more polyepoxides canalso be used in the practice of the present invention.

Other diepoxides which can be employed in the practice of the presentinvention include the diglycidyl ethers of dihydric phenols, such asthose described in U.S. Pat. Nos. 5,246,751; 5,115,075; 5,089,588;4,480,082 and 4,438,254, all of which are incorporated herein byreference, or the diglycidyl esters of dicarboxylic acids such as thosedescribed in U.S. Pat. No. 5,171,820. Other suitable diepoxides includefor example, αω-diglycidyloxyisopropylidene-bisphenol-based epoxy resins(commercially known as D.E.R.® 300 and 600 series epoxy resins, productsof The Dow Chemical Company, Midland, Mich.).

The epoxy resins which can be employed in the practice of the presentinvention also include the so-called “solid epoxy resins” preparedeither by reaction of diglycidyl ethers of dihydric phenols withdihydric phenols or by reaction of dihydric phenols with epichlorohydrin(also known as “taffy resins”).

Preferred epoxy resins useful in the present invention include, forexample, the diglycidyl ethers of bisphenol A; 4,4′-sulfonyldiphenol;4,4-oxydiphenol; 4,4′-dihydroxybenzophenone; resorcinol; hydroquinone;9,9′-bis(4-hydroxyphenyl)fluorene; 4,4′-dihydroxybiphenyl or4,4′-dihydroxy-α-methylstilbene and the diglycidyl esters of thedicarboxylic acids mentioned previously.

Other useful epoxide compounds which can be used in the practice of thepresent invention are cycloaliphatic epoxides. A cycloaliphatic epoxideconsists of a saturated carbon ring having an epoxy oxygen bonded to twovicinal atoms in the carbon ring for example as illustrated by thefollowing general formula:

wherein R is as defined above and n is as defined above.

The cycloaliphatic epoxide may be a monoepoxide, a diepoxide, apolyepoxide, or a mixture of those. For example, any of thecycloaliphatic epoxide described in U.S. Pat. No. 3,686,359,incorporated herein by reference, may be used in the present invention.As an illustration, the cycloaliphatic epoxides that may be used in thepresent invention include, for example,(3,4-epoxycyclohexyl-methyl)-3,4-epoxy-cyclohexane carboxylate,bis-(3,4-epoxycyclohexyl)adipate, vinylcyclohexene monoxide and mixturesthereof.

In general, the epoxy resin has a number average molecular weight ofless than 20,000, preferably less than 10,000, and more preferably lessthan 8,000. Generally, the epoxy resins useful in the present inventionhave an average molecular weight of from about 200 to about 20,000,preferably from about 200 to about 10,000, and more preferably fromabout 200 to about 8,000.

The epoxide equivalent weight of the epoxy resins is generally fromabout 100 to about 8000 and more preferably from about 100 to about4000. As used herein the terms “epoxide equivalent weight” refers to theaverage molecular weight of the polyepoxide molecule divided by theaverage number of oxirane groups present in the molecule. The preferreddiepoxides useful in the present invention are the epoxy resins havingan epoxy equivalent weight of from about 100 to about 4000.

The most preferred epoxy resin used in the present invention are theglycidyl polyethers of 2,2-bis(4-hydroxyphenyl)propane having an averagemolecular weight between about 340 and about 900 and an epoxideequivalent weight of between about 170 and about 500. Especiallypreferred are the glycidyl polyethers of 2,2-bis(4-hydroxyphenyl)propanehaving an average molecular weight of between about 340 and about 900,an epoxide equivalent weight of between about 170 and about 500, andcontaining from about 0.01% to about 1.0% weight or higher ofsaponifiable chlorine.

In general, the epoxy resin is used in an amount of from about 1 wt. %to about 99 wt. %, more preferably, from about 5 wt. % to about 95 wt. %and, most preferably, from about 10 wt. % to about 90 wt. %, based onthe weight of reactants.

In another embodiment, the instant invention is a nanocomposite polymer,made by the steps of: mixing the filler composition of the instantinvention with one or more polymer, polymer component, monomer orprepolymer to produce a polymer containing a filler having an averagesize of at least one dimension of the filler of less than two hundrednanometers upon examination by transmission electron microscopy of arepresentative sample of the polymer. Although not limited thereto, thepolymer can be selected from the group consisting of polyolefin polymersand copolymers, polyamide polymers and copolymers, polyester polymersand copolymers, polycarbonate polymers and copolymers, epoxy polymersand copolymers, styrenic polymers and copolymers, and mixtures thereof.

The epoxy resins of the present invention are useful, for example, inthe preparation of coatings, inks, resists, adhesives, moldings,composites, laminates, castings, pottings, and encapsulants.

EXAMPLE 1

4 g of montmorillonite (called “Pristine MMT) having a cation exchangecapacity of 92.6 meq/100 g (Cloisite Na Brand from Southern ClayProducts, Gonzales, Tex.) is dispersed in 400 g of water with mixingovernight to produce a first dispersion. The dispersion is centrifugedfor three hours at 4,400 gravity to form a gel-like product (called“g-MMT”) which is mixed with 400 mL of acetone, sonicated for one hourand mixed overnight to produce a second dispersion. The seconddispersion is centrifuged for three hours at 4,400 gravity to form agel-like product which is mixed with 400 mL of acetone, sonicated forone hour and mixed overnight to produce a third dispersion. The thirddispersion is centrifuged for three hours at 4,400 gravity to form agel-like product (called “n-MMT”) which is mixed with 400 mL of acetone,sonicated for one hour and mixed overnight to produce a fillercomposition of the instant invention.

EXAMPLE 2

The filler composition of Example 1 is sonication mixed with epoxy resin(DER 332 Brand diglycidyl ether of bisphenol epoxy resin from The DowChemical Company, Midland, Mich.) to form an epoxy resin mixture. Mostof the acetone is removed from the epoxy resin mixture by vacuumdistillation at 90° C. to produce an epoxy resin composition of theinstant invention.

EXAMPLE 3

The epoxy resin composition of Example 2 is mixed with4,4′-diamino-diphenyl sulfone (DDS) curing agent (Aldrich Chemical,Milwaukee, Wis.), poured into test bar molds and cured at 180° C. for 2hours followed by a post cure at 220° C. for 2 hours to produce testbars of an epoxy nanocomposite of the instant invention (called“epoxy/n-MMT”) containing 4.5% by weight of montmorillonite. FIGS. 1Aand 1B show a representative transmission electron micrograph of theepoxy nanocomposite of this invention.

COMPARATIVE EXAMPLE 1

Epoxy resin (DER 332 Brand diglycidyl ether of bisphenol epoxy resinfrom The

Dow Chemical Company, Midland, Mich.) is mixed with4,4′-diamino-diphenyl sulfone curing agent (Aldrich Chemical, Milwaukee,Wis.), poured into test bar molds and cured at 180° C. for 2 hoursfollowed by a post cure at 220° C. for 2 hours to produce test bars ofan epoxy polymer (called “Neat epoxy”) not containing any filler.

COMPARATIVE EXAMPLE 2

4 g of montmorillonite having a cation exchange capacity of 92.6 meq/100g (Cloisite Na Brand from Southern Clay Products, Gonzales, Tex.) isdispersed in 400 mL of acetone to form a dispersion of montmorillonitein acetone and then mixed with epoxy resin (DER 332 Brand diglycidylether of bisphenol epoxy resin from The Dow Chemical Company, Midland,Mich.) to form an epoxy resin mixture. Most of the acetone is removedfrom the epoxy resin mixture by vacuum distillation at 90° C. to producean epoxy resin composition. The epoxy resin composition is mixed with4,4′-diamino-diphenyl sulfone curing agent (Aldrich Chemical, Milwaukee,Wis.), poured into test bar molds and cured at 180° C. for 2 hoursfollowed by a post cure at 220° C. for 2 hours to produce test bars ofan epoxy nanocomposite (called “epoxy/d-MMT”) containing 4.5% by weightof montmorillonite. FIG. 2 shows a representative transmission electronmicrograph of the epoxy nanocomposite of this comparative example.

Testing

X-ray diffraction (XRD) patterns of the polymer samples are recordedusing a Bruker D8 diffractometer with Bragg-Brentano θ-2 geometry (40 kVand 40 mA) and a graphite monochromator. When running XRD on the g-MMTsample and the n-MMT sample, the samples were covered with Mylar brandX-ray film (from Complex Industries, Inc. Palm City, Fla.) to minimizeevaporation of water or acetone respectively from the samples.

Transmission electron microscopy (TEM) was performed on a JEOL JEM Brand1200 EX microscope operated at 100 kV. A Reichert-Jung Ultracut-E BrandMicrotome is used to prepare 70-100 nanometer thick section of thepolymer samples at room temperature for TEM imaging.

Dynamic mechanical analysis (DMA) is conducted using an RSA-III Brandinstrument (from TA Instruments) ranging from −120 to 250° C., at afixed frequency of 1 Hz and with a temperature increment of 5° C. perstep. A sinusoidal strain-amplitude of 0.05% was chosen for theanalysis. The maximum point on the tan δ curve is taken as the glasstransition temperature (T_(g)) of the sample.

Flexural moduli are measured following test method ASTM D790-96a usingan Instron Brand Model 4411 mechanical testing machine at a crossheadspeed of 0.127 cm/minute. Five tests are run for each polymer and theaverage value is reported.

The single-edge-notch 3-point-bending (DRN-3PB) fracture toughness ismeasured following test method ASTM D5045-96 using the linear elasticfracture mechanics (LEFM) approach using an Instron Brand Model 4411mechanical testing machine at a crosshead speed of 0.127 cm/minute atroom temperature. The test bars are notched with a jeweler saw, followedby tapping the crack tip with a liquid nitrogen chilled razor blade towedge open a sharp crack. Care is exercised to make sure the startercrack exhibits a thumbnail shape crack front before testing. The ratiobetween the crack length and the specimen width is held between 0.4 and0.6. Five tests are run for each polymer and the average value isreported.

The TEM analysis of freeze dried samples is one way to get at the sizeand degree of dispersion of the filler in a liquid comprising water.Rapid freezing is preferably employed to avoid crystalline ice formationthat tends to disrupt the three dimensional network. A small droplet ofthe dispersion is withdrawn using a pipette, rod or other suitabledevice and placed on a suitable carrier to include a TEM grid, a smallSEM sample stub or a copper top hat sandwich. The carrier compositionshould have good thermal conduction characteristics and its mass shouldbe kept to a minimum to optimize freezing rates. Quickly freeze thesample by rapidly immersing it into an appropriate cryogen like liquidpropane, nitrogen slush or spray the top hat sandwich with a pressurizedcryogen to obtain freezing rates of approximately 10,000° C./sec. Thesample is transferred in liquid nitrogen to a cryotransfer stage for theSEM or TEM or to a freeze drier. For the sample transfer stage methodone may either examine the sample in the frozen hydrated state with theuse of matrix sublimation to enhance contrast or expose detail or onemay freeze dry the sample in the microscope vacuum or suitable vacuumchamber. Images are preferably recorded in two or three dimensions forthe purpose of determining the shape and measuring the dimensions of thefiller. Charge compensation methods are preferably used, typicallyincluding operating at low accelerating voltages, the application of athin conductive metal coating or a low vacuum mode of operation or acombination of the above, to reduce sample charging in the SEMoperation.

Experimental Discussion

The following Table 1 lists the Glass Transition Temperature and StorageModuli data for the polymers tested.

TABLE 1 (Comparative (Comparative Example 1) Example 2) (Example 3) Neatepoxy epoxy/d-MMT epoxy n-MMT T_(g) (° C.) 228 225 228 Storage at 25° C.2.50 × 10⁹ 2.85 × 10⁹ 2.97 × 10⁹ modulus at 120° C. 1.80 × 10⁹ 2.06 ×10⁹ 2.31 × 10⁹ (Pa) at 250° C. 6.35 × 10⁷ 6.25 × 10⁷ 9.82 × 10⁷

The following Table 2 lists the Fracture Toughness and Flexural Modulusfor the polymers tested.

TABLE 2 (Comparative (Comparative (Example 3) Example 1) Example 2)Epoxy/n- Neat epoxy Epoxy/d-MMT MMT K_(IC) (MPa · m^(1/2)) 0.70 ± 0.030.97 ± 0.01 0.79 ± 0.02 Flexural Modulus (GPa) 2.67 ± 0.05 3.07 ± 0.133.62 ± 0.19

FIG. 3 shows the XRD patterns of n-MMT dried at 110° C., for n-MMT, forg-MMT dried at 110° C., for g-MMT and for Pristine MMT. FIG. 4 shows theXRD patterns of Epoxy/n-MMT, for Epoxy/d-MMT, for MMT mixed with epoxycuring agent DDS and for Pristine MMT. FIG. 5 shows the DMA scans forNeat epoxy, for Epoxy/d-MMT and for Epoxy/n-MMT.

Referring now to FIG. 3, the pristine MMT clay has a inter-galleryspacing peak at about 2θ=7.8°, which corresponds to an interlayerdistance of 11.3 Å. When the exfoliated clay nanoplatelets in water arecollected by centrifugation, there is still some water present in theg-MMT. The XRD pattern observed immediately after centrifugation isprincipally of amorphous characteristic, suggesting that the layeredstructure has exfoliated into XRD undetectable individual nanoplatelets.The sample of n-MMT in acetone shows a relatively sharp peak at 5.0°(17.7 Å) in XRD pattern. This indicates that during the solvent exchangeand centrifugation-redispersion steps, a large amount of acetonemolecules are trapped inside the collapsed clay gallery, which leads toa relatively large interlayer spacing. After such an exchange process,it is expected that most of the water molecules have been removed fromn-MMT. However, it is still anticipated that there may be a trace amountof remnant water trapped inside the MMT clay galleries. In order toconfirm this fact, both g-MMT and n-MMT are dried at 110° C. for 24hours. The XRD pattern of dried g-MMT shows a broad peak at a positionof 2θ=7.6° (11.9 Å), which has a slightly larger d-spacing than that ofthe pristine MMT clay probably because most of the water molecules haveescaped during the drying process. Only a very small amount of gallerywater molecules still stay within the layers, thus resulting in aslightly larger interlayer distance compared with the pristine MMT clay.After the n-MMT is dried at 110° C. for 24 hours, the XRD pattern showsa broad peak. However, the peak is located at about 2θ=7.8° (11.3 Å),which is almost the same as that of the pristine MMT clay. By comparingagainst the XRD of dried g-MMT, most water molecules in n-MMT have beenremoved after three additional centrifugation-redispersion steps.However, there appears to remain a trace amount of water, in n-MMT,which is evidenced by the broadening of the XRD peak, in comparison withthe pristine clay peak. This trace amount of water in n-MMT may stillgive rise to difficulties for the subsequent intercalation andexfoliation of clay in oganophilic monomers or polymers. Morecentrifugation-redispersion cycles may be needed in criticalapplications to further remove water in n-MMT if more optimumexfoliation of clay in the nanocomposite polymer is to be accomplished.The above XRD analyses suggest that g-MMT is in a nearly exfoliatedstate based on XRD and n-MMT is well-intercalated by acetone before theincorporation of epoxy resin. As will be shown later, this state ofintercalation is apparently beneficial in the preparation of epoxy/claynanocomposites.

It should be noted that if the exfoliated MMT nanoplatelets in aqueousdispersion are to be exchanged into a water-miscible organic solventthat has a boiling point much higher than that of water, then theorganic solvent can be directly mixed with the exfoliated MMT claynanoplatelets in water. Afterwards, the water can be removed by heatingthe mixture at a temperature above 100° C. to obtain exfoliated MMT claynanoplatelets in the organic solvent. In this case, nocentrifugation-redispersion step is needed for the preparation of n-MMT.

As described earlier, n-MMT is mainly wetted by acetone, although a verysmall amount of water still apparently remains. After n-MMT is mixedwith epoxy resin, it can be homogenously dispersed in epoxy with thehelp of mechanical stirring and sonication because epoxy monomer ismiscible with acetone. Even after the acetone is removed, the claynanoplatelets can still be uniformly dispersed in epoxy and no visiblephase separation is detected. It is noted that if the n-MMT is obtainedin less than 3 repeated centrifugation-redispersion cycles, then theepoxy/n-MMT will phase separate after acetone is removed. This findingsuggests that in order to prepare well-dispersed epoxy polymernanocomposites using the above approach, it is preferable to remove asmuch water from n-MMT as possible.

Referring now to FIGS. 1, 2 and 4, the morphological features ofepoxy/clay systems are characterized by XRD and TEM. The XRD data inFIG. 4 show that after the d-MMT is mixed with epoxy resin and thencured with DDS, the MMT clay peak is shifted to 2θ=5.8°, correspondingto an MMT clay interlayer d-spacing of 15.2 Å. This increased interlayerdistance from 11.3 to 15.2 Å is believed to be mainly caused by theintercalation of DDS in d-MMT. This conjecture is supported by the XRDpattern of MMT clay intercalated by DDS in acetone. This intercalatedcompound shows a peak at almost the same 2θ position as that ofepoxy/d-MMT. In the case of the epoxy/n-MMT system, only a broad andweak hump at about 2θ=4.5° is shown. This observation of weakdiffraction supports the belief that n-MMT can be intercalated andexfoliated by epoxy resin because of the presence of acetone inside theinterlayer galleries. Due to the presence of a trace amount of watertrapped inside the interlayers, some MMT clay particles may still stayloosely intercalated, which results in the observed broad and small humpat around 4° of the XRD pattern.

Referring now to FIGS. 1A and 1B, most MMT clay nanoplatelets areaggregated and form nano-tactoids, with dimensions of about 20 nm inthickness and about 1000 nm in length. Although the high aspect ration-MMT is not completely exfoliated to individual nanoplatelets, they arerandomly dispersed throughout the epoxy matrix. The incompleteexfoliation may be caused by the presence of a trace amount of waterinside the n-MMT galleries which prevents the complete insertion ofacetone and epoxy monomers. Referring now to FIG. 2, it will be notedthat the MMT clay nanoplatelets are even more highly aggregated thanshown in FIGS. 1A and 1B.

Referring now to FIG. 5, there are no significant differences in therubbery plateau moduli between neat epoxy and epoxy/d-MMT. However, inthe case of epoxy/n-MMT, the rubbery plateau modulus is about 60% higherthan those of neat epoxy and epoxy/d-MMT. This increase in rubberyplateau modulus is due to the presence of the relatively well-dispersedn-MMT nanotactoids in the epoxy nanocomposite of the instant invention.

A careful comparison of the storage moduli at various temperatures, asshown in Table 1 and FIG. 5 (upper curves), shows there are little or nodifferences in storage moduli between epoxy/d-MMT and epoxy/n-MMTsystems at low temperatures. However, as the temperature increases, thestorage modulus curve of epoxy/n-MMT begins to diverge from those ofneat epoxy and epoxy/d-MMT. The differences become greater and greater,and reach a maximum when the temperature rises above T_(g). The abovephenomena have been consistently observed in various exfoliated polymernanocomposites.

When organic cation modified MMT is used to prepare epoxynanocomposites, a significant decrease in T_(g) of epoxy nanocompositeshave been observed in the prior art. This drop in T_(g) is attributed inpart to the unwanted reactions between the mono-functional amine organicmodifiers and epoxy monomers, which lead to the formation of numerousdangling chain ends in the cured epoxy network. In this study, as shownin FIG. 5 and Table I, the T_(g) values of the three epoxy systems arepractically the same. Also, the Tan δ peak shapes around T_(g) among thethree epoxy systems are about the same, which signifies that the networkcharacteristics among the three systems are about the same. It is notedthat the retention of high T_(g) in epoxy/clay nanocomposite is asignificant advantage of the nanocomposite polymers of the instantinvention for structural and functional applications. Referring now toTable 2, the flexural modulus for Epoxy/d-MMT is increased by only 15%.However, the flexural modulus for Epoxy/n-MMT is increased 35% at roomtemperature. This increase is significant and is attributed to thehigher degree of exfoliation and dispersion of the MMT in Epoxy/n-MMTrelative to Epoxy/d-MMT even though the MMT is not fully exfoliated inEpoxy/n-MMT. The Mode-I critical stress intensity factor values forEpoxy/d-MMT show the K_(IC) value is increased by 39%. However, for theEpoxy/n-MMT system, the fracture toughness is slightly higher than thatof the neat epoxy. In the case of Epoxy/n-MMT, if all the n-MMTnanoplatelets were to be fully exfoliated, the K_(IC) values would beexpected to be the same as that of the neat epoxy. The presence ofnanotactoids in Epoxy/n-MMT can trigger limited crack deflection bydelamination. Thus, the small increases in K_(IC) values for Epoxy/n-MMTare expected.

Of particular significance, this disclosure demonstrates that it ispossible to significantly enhance the modulus of polymers by using theintercalating agent-free approach presented herein. Since this newapproach does not utilize any expensive, and sometimes toxic,organophilic surface modifiers, it is expected that physical properties,such as T_(g) and thermal stability, of the polymer nanocomposite can beretained. Most importantly, the manufacturing cost of preparing polymernanocomposites may be greatly reduced and become attractive forlarge-scale consumer products applications.

CONCLUSION

In conclusion, it should be readily apparent that although the inventionhas been described above in relation with its preferred embodiments, itshould be understood that the instant invention is not limited therebybut is intended to cover all alternatives, modifications and equivalentsthat are included within the scope of the invention as defined by thefollowing claims.

What is claimed is:
 1. A method for preparing a filler composition, thefiller composition useful to prepare a nanocomposite polymer, comprisingthe steps of: (a) dispersing a water dispersible filler material in aliquid comprising water to form a dispersion; (b) replacing at least aportion of the water of the liquid with an organic solvent so that thewater concentration of the liquid is less than six percent by weight toform the filler composition, the average size of at least one dimensionof the filler material being less than two hundred nanometers uponexamination by transmission electron microscopy of a representativefreeze dried sample of the dispersion of step (a), wherein the methoddoes not include a step of adding an intercalation agent to the waterdispersible filler, and the water dispersible filler material is acation exchanging layered material having a cation exchanging capacitythat is less than twenty percent exchanged with an organic cation. 2.The method of claim 1, wherein the cation exchanging layered material isselected from the group consisting of natural or synthetic bentonite,montmorillonite, hectorite, fluorohectorite, saponite, stevensite,nontronite, sauconite, glauconite, vermiculite, chlorite, mica,hydromica, muscovite, biotite, phlogopite, illite, talc, pyrophillite,sepiolite, attapulgite, palygorskite, berthierine, serpentine,kaolinite, dickite, nacrite, halloysite, allophane, immogolite,hydrotalcite, pyroaurite, calcite, wollastonite and mixtures thereof. 3.The method of claim 1, wherein the water concentration of the liquid isless than three percent by weight.
 4. The method of claim 1, wherein thewater concentration of the liquid is less than one percent by weight. 5.The method of claim 1, wherein the water concentration of the liquid isless than one half percent by weight.
 6. The method of claim 1, whereinthe water concentration of the liquid is less than one tenth percent byweight.
 7. A method for preparing a nanocomposite polymer by the stepsof: preparing a filler composition according to the method of claim 1;and mixing the filler composition with one or more polymer, polymercomponent, monomer or prepolymer to produce a polymer containing afiller having an average size of at least one dimension of the filler ofless than two hundred nanometers upon examination by transmissionelectron microscopy of a representative sample of the polymer.
 8. Themethod of claim 7, wherein the monomer comprises an epoxy resin andwherein the filler composition is mixed with the epoxy resin to form amixture, which mixture is then devolatilized to remove organic solventand then cured to produce an epoxy nanocomposite polymer.
 9. A methodfor preparing a filler composition, the filler composition useful toprepare a nanocomposite polymer, comprising the steps of: (a) dispersinga water dispersible filler material in a liquid comprising water to forma dispersion; (b) replacing at least a portion of the water of theliquid with an organic solvent so that the water concentration of theliquid is less than six percent by weight to form the fillercomposition, the average size of at least one dimension of the fillermaterial being less than two hundred nanometers upon examination bytransmission electron microscopy of a representative freeze dried sampleof the dispersion of step (a), wherein the method does not include astep of adding an intercalation agent to the water dispersible filler,and the water dispersible filler material is a cation exchanging layeredmaterial having a cation exchanging capacity that is essentially free oforganic cation.
 10. The method of claim 9, wherein the cation exchanginglayered material is selected from the group consisting of natural orsynthetic bentonite, montmorillonite, hectorite, fluorohectorite,saponite, stevensite, nontronite, sauconite, glauconite, vermiculite,chlorite, mica, hydromica, muscovite, biotite, phlogopite, illite, talc,pyrophillite, sepiolite, attapulgite, palygorskite, berthierine,serpentine, kaolinite, dickite, nacrite, halloysite, allophane,immogolite, hydrotalcite, pyroaurite, calcite, wollastonite and mixturesthereof.
 11. The method of claim 9, wherein the water concentration ofthe liquid is less than three percent by weight.
 12. The method of claim9, wherein the water concentration of the liquid is less than onepercent by weight.
 13. The method of claim 9, wherein the waterconcentration of the liquid is less than one half percent by weight. 14.The method of claim 9, wherein the water concentration of the liquid isless than one tenth percent by weight.
 15. A method for preparing ananocomposite polymer by the steps of: preparing a filler compositionaccording to the method of claim 9; and mixing the filler compositionwith one or more polymer, polymer component, monomer or prepolymer toproduce a polymer containing a filler having an average size of at leastone dimension of the filler of less than two hundred nanometers uponexamination by transmission electron microscopy of a representativesample of the polymer.
 16. The method of claim 15, wherein the monomercomprises an epoxy resin and wherein the filler composition is mixedwith the epoxy resin to form a mixture, which mixture is thendevolatilized to remove organic solvent and then cured to produce anepoxy nanocomposite polymer.